The invention relates to a plant for utilizing the energy in the waves which are present at a given time in a section of a water area such as an ocean or a lake, and comprising a base located in this section and in the shape of a platform or raft and a wave converter placed on the base and serving for transforming the wave motion of the water into whirling motion.
U.S. Pat. No. 4,152,895 discloses a plant with a turbine powered by wavy water transformed into whirling water by means of a wave converter. This converter consists mainly of a horizontally orientated whirl pipe with an elongated gill situated at the water surface. The water of the waves is led via a ramp tangentially in through the gill and is thereby set in whirling motion in the whirl pipe. The whirling water drives the turbine which is situated at an open end of the pipe.
This known plant is only able to utilise the energy in small waves of the kind that is formed in shallow water across a gradually slanting ocean floor. The coefficient of utilisation is low. The static energy of the waves is only utilised to a modest extent. Large waves wash over the plant without contributing particularly to the output of the plant.
The applicant""s EP Patent No 0 611 418 B1 which is included in the present application as reference discloses a wave converter situated on a moored raft. The wave converter has a whirl pipe with a longitudinal slot and a wave catch consisting of a number of catch plates which in pairs define elongated channels for leading the water of the waves mainly tangentially into the whirl pipe with increasing velocity. Thereby, the water is made to flow through the whirl pipe in a whirling motion. The whirl pipe is open at both ends, and at each of these ends is placed a energy-converting machine in the shape of e.g. a turbine driven by the whirling water and driving a generator.
This wave converter can utilise the static and dynamic energy of the waves both in shallow and deep water with a large output. The size of the waves that are effectively caught and utilised is set by the dimensions of the plant alone and especially by the height of the wave catch.
A wave converter can be described as a machine which, without any movable parts, transforms the waves into a rotating water flow, which is directly well suited for driving a rotating machine, e.g. a turbine.
Normally, a machine only functions optimally within a specific operating range. Outside this, the machine will be functioning with reduced output.
However, wave energy is not a constant quantity which can form part in optimal placing of a plant. Sometimes, there is hardly any energy while there at other times will be very large amounts of energy available. A given plant will therefore not be able to fully utilise the wave energy which on average is available in a water area.
Normally, the relation between output and investment grows advantageously with the size of the plant. In many cases, it pays to build large plants. However, a large rotating machine, such as a turbine equipped with a generator, costs more than a number of smaller machines with a corresponding total capacity.
The object of the invention is to provide a plant of the kind mentioned in the opening paragraph, which can utilise the energy of the waves with a larger output than known so far.
A second object of the invention is to provide a plant of the kind mentioned in the opening paragraph, which can produce a given output with less construction costs than known so far.
The novel and unique features according to the invention, whereby this is achieved, is the fact that the plant furthermore comprises at least two adjacent wave catches each having at least one catch plate for catching at least a part of the water of the waves and making this water flow down along the catch plate from a top front edge to a bottom rear edge on the plate, and one whirl pipe for each wave catch for, via a slot extending along the rear edge of the at least one catch plate, taking up the water flowing along the catch plate so that this water will describe a whirling motion in the whirl pipe.
This wave converter can advantageously be arranged with a number of small and therefore relatively inexpensive energy converting machines whether the wave catches are placed in a row next to or behind each other.
In the last-mentioned case, the front edge on the catch plates of each wave catch can be situated higher up than the front edge on the catch plate of the preceding wave catch whereby a number of conversion steps are created that set in as the amplitude and energy content of the waves increase. Thereby, the energy of the waves can be utilised optimally over a very large interval.
In order to prevent that some of the water of the waves run unutilised down between the wave catches, each wave catch can be provided with a cover plate situated close to or in contact with the rearmost catch plate in the preceding wave catch. The cover plates ensure that the water of the passing waves is led into the wave converter without any waste.
In the cases where the wave catches of the wave converter are placed in a row behind each other, the wave converter will, for practical reasons, be formed with a limited number of conversion steps, e.g. two, three, or four. The steps begin functioning one after another as the amplitude of the waves increases. As mentioned above, the energy of the waves is utilised within a very large interval.
Due to the limited number of steps of the wave converter, the utilisation will however occur by jumps. Between these jumps, situations may arise where one or potentially several of the rearmost steps do not receive sufficient water and thereby energy to function satisfactorily.
In order to avoid that the total output of the plant is thereby reduced, at least some of the wave catches of the above rearmost steps can be arranged with a damper arranged to, in case of no or less influx of water to the step, shut off the flow between two catch plates or between a cover plate and a catch plate and, in case of influx of water above a pre-fixed limit, open up for such a flow. At the same time, a channel can be placed above said damper, said channel is extending between two adjacent wave catches.
When a step receives sufficient energy-containing water, the damper opens, and the step is functioning normally. If the influx of water is below a pre-fixed limit, the damper is closed whereby the water in the step via the channel runs down into the preceding step(s) in order to be utilised here.
The wind sets the water into wavy motion and during this gives up a part of its energy to the water.
The wavy water has the advantageous characteristic that it can accumulate the received wind energy. The waves will continue to roll even long time after the wind has dropped. The waves are therefore a far more stable energy source than the wind.
However, the energy pulsates with the frequency of the waves. A rotating machine will normally not be able to follow this frequency, i.e. change the number of revolution at the same rate, and its performance will therefore not be optimally. Furthermore, the intermittent stress is not good for the machine.
However, the pulsations are smoothed to some extent in the whirl pipe owing to the fact that the whirling water in these acts as flywheels which soften the shocks.
This advantageous flywheel effect can be enhanced by means of turbine pipes each constituting an extension of a whirl pipe, and/or by means of a tubular manifold for taking up the whirling water from several whirl pipe. In this case, an energy converting machine is placed at the open end of the whirl pipes or the manifold. The effect is especially great when the whirl pipes and/or manifold are long.
The flywheel effect can be further enhanced by giving the whirl pipes and/or manifold a larger diameter along at least a part of the length. On this part, an extra amount of energy is stored for smoothing the pulsating wave energy.
Furthermore, the whirl pipes and/or manifold can be completely or partly formed with an resilient wall for absorbing the pulsations.
The whirl pipe of the known plant of the above EP Patent No 0 611 418 B1 ends at each end via a turbine pipe in a diffuser tower extending downwardly to calm water. Thereby, it is avoided that on the discharge end of the turbine, damaging pressure impulses are generated which could make the turbines function irregularly.
In order to reduce construction costs, the whirl pipes for the plant according to the invention can via turbine pipes end in a joint diffuser tower.
When this tower is placed at or near the centre of gravity of the wave converter, the tower furthermore serves for keeping a floating plant stable in the water.
If the wave converter is standing on a platform, the diffuser tower can be a leg carrying the platform and at a suitable distance below the surface of the water, having an opening for passage of the water from the whirl pipes.
Such a diffuser tower can be connected to the whirl pipes via curved or helical turbine pipes. Thereby, the turbine pipes obtain a great length, and they can therefore contain a correspondingly large amount of whirling water to, as flywheels, effectively soften the shocks from the pulsating wave energy.
The invention will be explained in greater detail below, giving further advantageous characteristics and effects and describing only exemplary embodiments with reference to the drawing, in which